Fluid amplifier



May 5, 1970 MQNGE ET AL FLUID AMPLIFIER 4 Sheets-Sheet 1 Filed July 22, 1966 May 5, 1970 MONGE ET Al.

FLUID AMPLIFIER 4 Sheets-Sheet 2 Filed July 22, 1966 May 5, 1970 MQNGE ETAL 3,509,898

FLUID AMPLIFIER Filed July 22, 1966 4 Sheets-Sheet s May 5, 1970 M. MONGE ET AL FLUID AMPLIFIER 4 Sheets-Sheet 4 Filed July 22, 1966 United States Patent Office U.S. Cl. 137-815 14 Claims ABSTRACT OF THE DISCLOSURE A fluid amplifier that provides a sensitive switching function including basically a planar fluidic amplifier having a supply passage that directs fluid selectively to first and second outlet passages, these passages being arranged so that the supply flow normally exits from the first outlet so that the device has monostable characteristics, there being provided a control passage for conveying control fluid which directs the supply fluid from the first passage to the second passage which is the passage conveying fluid to a load, the first outlet passage being directed back in opposed relation to the control fluid passage so that it in effect assists the monostable characteristics of the device and renders the device sensitive to a predetermined control pressure to switch from the first outlet passage to the second utilization outlet passage.

This invention relates to fluid amplifiers utilizing the principle of interaction of two or a plurality of fluid jets, such as water or air, for accomplishing various functions, such as signal amplification and detection, and various logical functions equivalent in all to those currently carried out by electronic systems.

An object of this invention is to provide a fluid amplifier acting as a relay, in which the switching operation function takes place without the use of any moving part by snap action on or oil similarly to the operation obtainable by means of electric relays or thyratrons.

A further object of this invention is to provide a fluid amplifier operating as a relay, the switch point of which is adjustable throughout the range of variation of the input signal, the output signal being of improved stability, and the sensitivity of the switch point being improved with respect to relays having mechanical moving parts known in the art of pneumatic instrumentation.

A further object of this invention is to utilize a fluid amplifier operating as an adjustable trigger relay for switching over electric contacts in a power switch.

A further object of this invention is to utilize a fluid amplifier operating as an adjustable trigger relay for accomplishing the proximity alarm function, wherein setting of the alarm distance is variable without the use of mechanical moving parts or without parts contacting the body to be signaled.

A further essential object of this invention is to utilize a fluid amplifier operating as a relay for accomplishing the function of input signal delay with adjustable delay time.

A further object of this invention is to utilize a fluid amplifier operating as a relay for obtaining a variable frequency oscillator.

The specific nature of this invention as well as further uses, applications and advantages shall be further explained in the course of the appended detailed description relating to the accompanying drawings, which show by way of non-limiting examples preferred embodiments thereof.

FIG. 1 is a side view of a preferred embodiment of the fluid amplifier according to this invention;

3,509,898 Patented May 5, 1970 FIG. 2 is a sectional view on line II of FIG. 1;

FIG. 3 is a sectional view on line IIIIII of FIG. 2;

FIGS. 4 and 5 are sectional views showing the operation of the amplifier according to this invention;

FIGS. 6 and 7 show the combination of an amplifier according to this invention with an electric switch;

FIG. 8 shows the use of the combination according to FIGS. 6 and 7 in connection with a machine tool;

FIG. 9 shows the use of a plurality of fluid amplifiers according to this invention in connection with an automation box;

FIG. 10 shows the use of a fluid amplifier according to this invention for providing a distance detector;

FIG. 11 shows the use of a fluid amplifier according to this invention for providing a delay relay;

FIG. 12 shows the use of an amplifier according to this invention for providing an oscillator.

The fluid amplifier denoted by 1 comprises three planar plates 2, 3 and 4 forming a sandwich held together by means of suitable screws 5 or adhesives or other conventional fastening means. The plates 2, 3 and 4 may be made of any suitable metallic, plastic or ceramic material. The plates 3 are formed with:

(a) a main conduit 12 for the working fluid input;

(b) an output conduit 13 for the working fluid, having its axis angled with respect to the axis of the input conduit 12;

(c) a conduit 14 for a control fluid having its axis substantially orthogonal to the axis of the main conduit 12, situated at an angle exceeding to the axis of the output conduit 13; a feedback conduit 15 branched from the region of convergence 16 of the three conduits 12, 13 and 14 and having the axis of its pick-up section lying between the axes of the output conduit 13 and control conduit 14.

The feedback conduit 15 opens into the region of convergence 16 by a delivery section 17 having its axis substantially orthogonal to the axis of the main conduit and opposed to the control conduit 14.

The adjacent walls of the output conduit 13 and of the pick-up section of the feedback conduit are interconnected by a section 18 acting as flow divider.

The main conduit 12 is off-set with respect to the divider 18 so that in the absence of a fluid stream in the control conduit 14, the working fluid fed to the main conduit 12 tends to flow through the feedback conduit 15 in a closed cycle, whereas in the presence of a fluid stream of suflicient power in the control conduit 14 the working fluid from the main conduit is deflected to the output conduit 13. A bleed valve 19 is interposed in the feedback conduit and is controlled by a needle screw 20 formed with a conical end section.

The conduit 15 includes past its pick-up section an enlarged section in which the bleed valve 19 is provided.

The section 18 acting as flow divider includes a concave wall having its concavity turned towards the fluid supply from the main conduit and forming with the contiguous walls of the feed back conduit 15 and discharge conduit 13 two flow-dividing edges turned towards the outlet opening of the main conduit 12.

The plate 4 is formed with tapped holes adapted to receive nipples for the interconnecting pipes through which a pressure fluid is admitted into the conduits formed in the plate 3. Any working fluid of a gaseous nature such as air or of a liquid nature such as water or oil may be employed.

The fluid amplifier 1 is fed with working fluid through the nipple 6 and interconnecting pipe 7 from a pressure source 8, it being understood that the desired pressure of the working fluid may be obtained by means of a conventional pressure reducer well known in the art of pneumatic instrumentation.

By the nipple 9 and pipe 10- the fluid amplifier may be connected to a source of pressure 11 which supplies fluid for the control signal. The control signal may be any pressure signal adjustable throughout the Working range of the amplifier e.g. by means of a pressure reducer. With the adjusting screw 20 the switching point of the amplifier 1 may be varied throughout the working range of the latter.

The nipple 14' acts as an output for the element, from which a signal on or off is obtained as a function of the working point of the amplifier 1.

The operation of the device will be better understood from the following description referring to FIGS. 4 and 5.

The pressure fluid from the source of supply 8 is admitted to the conduit 12 from which it flows to the region of convergence 16. The control fluid is admitted to the conduit 14 from which it flows to the region of convergence 16 to deliver a control signal.

When there is no control signal present, the working fluid jet issuing from the conduit 12 is nearer the sidewall 24 of the conduit than to the wall 25 of the conduit 13 and sticks to the wall 24 by the Coanda effect well known in the art of fluid amplification and is recycled through the conduit 15.

FIG. 4 shows the configuration taken by the working fluid stream in the absence of a control signal. The fluid jet issuing from the end section 17 of the feed back conduit 15 acts at the region 16 on the working fluid issuing from the main conduit 12, whereby the sticking effect to the sidewall 24 is increased, the whirl 26 forming at the region of the divider 18 promoting the stability of the working fluid stream. Consequently, no fluid flows through the conduit 13 and there is no output signal.

In other words, the effect due to the positive feed back of fluid in the conduit 15 together with the geometrical off-set of the axis of the main conduit 12 and divider 18, keeps the fluid stream sticking to the wall 24 so that, in the absence of the control signal, there is no output signal.

When a control signal is delivered through the conduit 14 the fluid issuing from the main conduit 12 is subjected to the resultant action of two jets, namely the positive feedback jet issuing from the section 17 and the control jet issuing from the conduit 14. The jet issuing from the main conduit 12 sticking to the wall 24 keeps in this position as long as the control signal is lower or, at the limit, equals the feedback signal, inasmuch as the differential pressure acts on the fluid jet issuing from the main conduit in the sense of promoting its sticking to the wall 24. Consequently, there is no output signal from the conduit 13 as long as the control signal pressure is lower than or the same as the feedback pressure. When the control signal pressure exceeds the feedback pressure, the resultant differential pressure acts to release the fluid from the wall 24 and tends to deflect it towards the wall 25 of the output conduit 13 of the amplifier. The fluid then starts moving towards the region of convergence at the divider 18. However, this position is unstable, inas much as the feedback stream recovered through the conduit 15 decreases, thereby immediately causing a decrease in the quantity of motion of the feedback jet acting on the right-hand side of the main jet. The differential pressure acting on the main jet thereby increases and further deflection towards the wall 25 ensues. This process is self-enhancing, so that the main jet is switched over to the output conduit 13.

Thus, whenever the control signal exceeds the value of the feedback signal, the main jet is switched from its initial position to its switched-on position by a peculiar snap action similar to that of conventional relays.

FIG. 5 shows the configuration taken by the fluid stream in the fluid amplifier in a switched-on position. The jet keeps stable in this new position since the feedback has decreased and the differential operating pressure 4 acts to maintain the jet sticking to the wall 25. The fluid stream issuing from the conduit 13 can be variously utilized as a power signal.

When the control signal decreases and sinks below the positive feedback value, owing to the decrease in control signal the main jet tends to be removed from the wall 25, the feedback value starts increasing and the differential pressure consequently rises and effects a further deflection of the jet towards the wall 24 which causes the jet to stick to the latter wall. The amplifier output then becomes zero.

The amplifier 1 is therefore monostable with positive feedback in operation and snappingly accomplishes the on and off function similarly to certain pneumatic relays known in the art of pneumatic instrumentation; the snapping operation depends only upon the pressure gradient occurring transversely of the power jet and not upon the level of the control pressure so that by varying the feedback value it is possible to vary the control pressure with respect to which the peculiar snap-action switching over of the amplifier is performed. The switching point can be set within a wide range of variation in control pressure by varying the bias of the feedback by means of the screw 20 which affords continuous variation in bias. The bleed valve 19 controlled by screw 20 acts as a variable resistor by which a more or less large fraction of the feedback stream can be discharged to the outside to thereby decrease or increase at will the pressure level in the end section 17 of the feedback conduit 15.

The operational characteristics of an amplifier according tothis invention are given by way of example.

The monostable variable positive feedback fluid amplifier is fed with a pressure of 20 p.s.i. (an exemplary feed pressure for pneumatic instruments known in the art). Under these conditions the switching point can be con tinuously adjusted throughout the range in variation from 3 to 15 p.s.i. (which is the standard range of pneumatic instruments) with a setting accuracy of the switching point within 2 cm. water column. This high accuracy, greater than with conventional pneumatic relays having mechanical moving parts, together with the constancy in setting with time make the variable positive feed-back fluid amplifier more particularly suitable for use instead of conventional pneumatic relays.

In a large number of cases the active output of the amplifier according to this invention may be directly utilized either as pressureor delivery signal for operating control members, intercepting valves, pneumatic cylinders, etc.

It may, however, be desirable to obtain, at the switch over of the amplifier, an electric signal.

To this end the amplifier is combined with an electric switch as shown in FIGS. 6 and 7. Referring to FIG. 6, the output conduit is connected by a further conduit 28 to one end of an elongated chamber 29 freely accommodating a ball 30, which may be of stainless steel or any other material. The other end of the chamber is open to let the ball 30 through. In proximity to the chamber 29 a microswitch 31 is attached, the operating lever 32 of which bears on the ball 30 preventing escape thereof from the chamber 29. A suitable clearance between the ball 30 and sidewall of the chamber 29, which acts as a fluid output impedance allowing a certain flow of air to the outside, causes the ball to constantly remain floating in contact with the microswitch operating lever. In addition, friction between the ball and seat therefor is avoided.

As switch-over of the amplifier 1 occurs dependently upon the predetermined switching point, the working fluid deflected to the outlet conduit 13 impinges upon the ball 30 and acts thereon by a force which depends upon the effective ball surface and pressure of the output jet.

The ball is therefore pushed back by a force which is sufficient to effect closure of the microswitch 31 through the lever 32. At a predetermined pressure, which is variable by means of the screw 20 throughout the working range of the amplifier, an electric power signal is therefore delivered, which is adapted to directly operate re- ,mote control switches, lamps, alarm systems, etc.

Transduction of the' signal issuing from the amplifier 1 to an electric signal may moreover be obtained by means of the output fluid from the amplifier or by other means known in the art, such as actuation of a reed switch by means of a permanent magnet; in this case the ball 30 is replaced by a permanent magnet.

The electric output signal may moreover be obtained without the use of moving mechanical parts by means of hot wire thermistors or anemometers, such as 33 in FIG. 7, adapted to signal the flow of fluid possessing a certain velocity.

By way of example, without intending hereby to restrict the uses of the fluid amplifier according to this invention which, when provided with an electric output accomplishes a function similar to electropneumatic relays with adjustable switching point, a special configuration of apparatus shall now be described which is known in the art of pneumatic dimensional gauging as automation box for machine tools for continuous control of machining of workpieces, utilizing fluid systems.

By automation box a pneumatic apparatus is understood hereafter, which comprises one or a plurality of pneumatic units for measuring size, known in the art, in which to the variation in a size there corresponds a variation in pressure proportional thereto. This pressuremodulated signal is sent to one or a plurality of electropneumatic relays which supply an electric output signal at a predetermined value of dimensional size.

These electric outputs may directly operate remote control switches controlling the cycle of a machine tool.

It is thereby possible by measuring by means of a suitable pneumatic system the workpiece during machining, to automatically operate the rough machining controls, finishing controls, etc.

This affords a self control of the machine tool, the product ion being maintained within required allowances.

FIG. 8 shows by way of example only a possible arrangement of the automation box for machine tools utilizing fluid amplifiers according to this invention.

In this automation box the pressure from the measuring circuit which includes a pressure reducer 34, an adjustable throtle 35 and a measuring nozzle 36, is transmitted to an indicator 37 which may be of the Bourdons tube or water column type.

The pressure is further sent to the control conduits of two fluid amplifiers denoted by 38 and 39 of the adjustable positive feedback type, provided with an electric or electronic output stage, adapted to directly drive both conventional machine control switches, magnetic valves and other control members.

The fluid amplifiers 38, 39 yield at a predetermined value of the size taken by the workpiece being machined an electric output capable of effecting stoppage of the working cycle of the machine tool according to a predetermined sequence, which may be adapted to the type of machine tool. For instance, in grinding machine, at the roughing out stage, when the size of the workpiece is reduced to a pre-established roughing out limit, the positive feedback fluid amplifier, which has been previously set at this value, switches over.

The effective output from the fluid amplifier 38 effects then through a microswitch stoppage of the roughing out operation and starting of the finishing operation. When the size of the workpiece is reduced to the limit set for finishing, switching over of the second amplifier 39, which has been previously set to this value, effects stoppage of the grinding cycle.

The use of the adjustable positive feedback fluid amplifier in connection with automation box affords, in addition to higher accuracy and life, a safer operation due to total absence of moving parts. By adapting the system of integrative circuits known in electronics as applied to fluid systems, the whole automatic measuring and check circuit can be provided on one panel 41 only. In this case the automation box appears as shown in FIG. 9.

The fluid amplifier according to this invention is suitable for wide use in all pneumatic dimensional gauging operations, such as automatic selection and classification in classes, post-process testing, etc.

It may often be necessary to signal the presence of a workpiece without coming into contact with the surface thereof; electric, electronic and pneumatic systems accomplishing this function are known in the art.

The fluid amplifier according to this invention may be employed for signaling the passage or presence of a workpiece. In this case the adjustable positive feedback fluid amplifier acts as a proximity alarm and is arranged as shown in FIG. 10.

Referring to FIG. 10, an outwardly opening pipe 41 is branched on the main conduit 12, provided with a nozzle 42 and a throttle 43 intermediate its free end and the main conduit 12.

The control conduit 14 is branched from a section of the branch pipe 41 between the throttle and nozzle 42. The nozzle 42 cooperates with the surface of a workpiece 44 in order to determine the distance of the latter.

If no surface faces the nozzle 42 which acts as sensor for the workpiece 44 to be signaled, the stream from the branch pipe 41 through the throttle 43 is free to flow to the outside through the nozzle 42. The static pressure value built up in the conduit 14 is therefore rather low. This pressure is used to provide the amplifier control signal. By acting on the adjusting screw 20 which sets the value of the feedback pressure, in the absence of a workpiece in proximity to the nozzle 42 the main stream is switched over and the effective output of the amplifier is consequently zero.

Where any surface is in proximity to the sensing nozzle 42, the presence of the said surface prevents free flow of the stream through the nozzle, consequently increases the static pressure in the section between the throttle 43 and conduit 14. Whenever the static pressure in the conduit 14 equals or exceeds the value of the feedback pressure, it switches over the stream in the main conduit, so that a pressure signal arises at the amplifier output whenever any surface is within reach of the sensing nozzle 42. The pressure signal may be utilized in various manners known in the art for either signaling, such as by means of lamps or other alarm system, the presence of the workpiece or directly drive pneumatic control or safety devices. By varying the value of the feedback it is further possible to vary the nozzle-to-surface spacing upon which the desired proximity alarm is dependent.

A further modification of the circuitry of the fluid amplifier according to this invention will afford a delay function.

In a large number of cases, more particularly in electronic circuit technique, it becomes necessary to utilize a component comprising an input and an output capable of generating an output signal whenever an input signal is present. As the input signal ceases, the output remains eflective during a certain time which may be adjustable within wide limits, on expiry of which it is annulled.

FIG. 11 shows a delayed time relay for carrying out the above described function by utilizing a fluid amplifier, more particularly an adjustable positive feedback monostable fluid amplifier according to this invention.

In the diagram shown in FIG. 11 a source of pressure 45 is connected by an intercepting valve 46 to the end of a pipe 47 from which a tank 48 is derived. The other end of the pipe 47 is connected with the control conduit 14 of the amplifier 1.

A throttle valve 49 adjustable in cross sectional area is interposed between the connection for the tank 48 in the pipe 47 and amplifier 1.

In the absence of the control signal from the source 45 the working fluid stream steadily circulates in the feedback conduit of the amplifier 1, so that the amplifier out:

put is zero. By opening the intercepting valve 46, the pressure signal is connected through tank 48 and adjustable throttling valve 49 with the input to the amplifier 1 and effects switching over.

This results in a pressure signal, which may at will be amplified, at the effective output of the amplifier.

The output signal remains stable throughout the duration period of the control signal. When the control signal is shut off by closing the valve 46, the output signal tends to keep stable in this condition because the static pressure in the tank 48, hence in the control conduit of the amplifier 1, exceeds the feedback value.

The working fluid stream which is thus switched over to the effective output of the element has a constant mean velocity V and therefore sets up a constant suction at the interaction zone between the control conduit and main conduit.

Consequently, the pressure in the tank 48 tends to sink and discharge fluid through the variable throttle 49 at a velocity depending both on the value of the resistance imposed by the throttle itself and on the suction level of the main stream.

At the discharge stage of the resistance-capacitor circuit between the intercepting valve 46 and control conduit of the fluid amplifier 1, as the static pressure in the tank 48 sinks below the value of the feedback pressure acting on the main stream, the main stream is again switched over to the inoperative condition, the effective output being annulled. The delay by which the output signal is annulled on annulling of the input signal therefore merely depends upon the time necessary for discharging the tank 48 through the variable throttle 49 and control conduit, and is therefore steadily adjustable by acting on the value of the variable throttle.

The delay effect on the output signal is thereby obtained by utilizing the fluid amplifier according to this invention without employing any moving mechanical part. Moreover, since the sucked air delivery at the interaction region of the main stream is constant, a high accuracy in reproducibility of the delay times is afforded.

This effect may be widely used wherever it is necessary to extend the duration period of the output signal even in the absence of the input signal and obtain after a certain period, which is variable at will, automatic zeroing of the output without having recourse to any external signal for re-setting.

A further use of the amplifier according to this invention is the combination with a blind bottom conduit for accomplishing the function of variable frequency oscillat'or similar to the function of conventional electronic oscillators. A possible configuration of the oscillator employing the fluid amplifier is given in FIG. 12, in which the feedback conduit 15 is deprived of its bleed valve.

The value of the pressure in the feedback conduit 15 is therefore constant and reaches its maximum value admitted by the recovery capacity of the conduit 15. The control conduit 14 is connected with a conduit 50 of a predetermined length closed at its end by an intercepting valve 51. When the amplifier 1 is fed, the main fluid flows through the feedback conduit 15 and is returned to the input thereby increasing the sticking effect of the main stream to the sidewall 24. The fluid portion from the main stream that cannot be carried along to the output by the stream in the conduit 15 fills by flowing through the conduit 14, the conduit 50 which performs an inertance function similar to the inductance in electric circuits.

A pressure wave is thereby set up in the conduit 50 and propagates at a velocity depending upon the pressure gradient set up in the inertance, reaching the closed end of the conduit 50, and is thereafter reflected and returned towards the conduit 14 of the amplifier 1. The pressure wave arriving in the conduit 14 effects switching over of the main stream towards the output of the amplifier 1 at which a pressure signal is given.

However, this new position is not stable for, as soon as the main stream has been removed from the wall 25, the pressure wave set up at the output section of the conduit 14 is annulled at the interaction region and removes the cause for switching over the jet. The positive feedback restores the main stream to its inoperative position, whereupon the process described above starts again.

Consequently, owing to the compression and rarefaction of the fluid in the inertance comprising the conduit 50, the jet oscillates between the two positions at a constant frequency depending merely upon the time taken by the pressure wave to flow through the whole path to and fro in the conduit '50. By varying the length of the conduit 50 it is therefore possible to vary the frequency of oscillation. As a result, at the output of the amplifier 1 a pulsating pressure signal arises, the frequency of which is constant and independent within wide limits from the output load.

Because of the absence of any moving part the fluid oscillator is advantageous in that it can be employed in the low frequency range by inserting suitable inertances, comprising for instance turns in the calibrated length conduit 50.

What we claim is:

1. Fluid amplifier of the type comprising a main input conduit for a working fluid, an output conduit for said working fluid having its axis deflected from the axis of the input conduit, utilization means for working fluid from said output conduit and a conduit for a control fluid having its axis substantially orthogonal to the axis of the main conduit and at an angle exceeding to the axis of the output conduit, a feedback conduit branched adjacent the zone of convergence of the three above mentioned conduits and having an axis lying between the axes of the output conduit and control conduit, said working fluid being adapted to be directed to the output conduit or the feedback conduit, said feedback conduit opening into the region of convergence of the above mentioned conduits by an end section having its axis substantially orthogonal to the axis of the main conduit and opposed to the control conduit; said feedback conduit constructed to feedback substantially all of the fluid in said feedback conduit toward said region of convergence, the adjacent walls of the output conduit and the feedback conduit being interconnected by a section acting as a divider; the

' configuration of the region of convergence of the conduits being such that in the absence of a fluid stream in the control conduit, the working fluid fed to the main conduit tends to flow through the said feedback conduit in a closed circuit, whereas in the presence of a fluid stream of sufflcient power in the control the working fluid from the main conduit is deflected to the output conduit.

2. Fluid amplifier as claimed in claim 1, including a discharge opening to the outside of said amplifier provided in the feedback conduit and controlled by adjusting means adapted to vary its cross sectional area in order to vary the fluid pressure from the feedback conduit which acts on the working fluid stream from the main input conduit.

3. Fluid amplifier as claimed in claim 1 wherein said feedback conduit has an enlarged section in which the said opening controlled by adjusting means is formed.

4. Fluid amplifier as claimed in claim 1, wherein said divider between the adjacent walls of the output conduit and feedback conduit includes a concave wall turned with its concavity towards the inflow of fluid from the main conduit and forming together with the contiguous walls of the feedback conduit and discharge conduit two dividing edges turned towards the output of the main input conduit.

5. A fluid amplifier as defined in claim 1, including an electric switch provided with a movable operating member situated in the path of the fluid issuing from the output conduit of the amplifier.

6. A fluid amplifier as defined in claim 1, including an electronic detector essentially comprising a thermistor situated in the path of the fluid issuing from the output conduit.

7. A fluid amplifier as defined in claim 1, including means for measuring workpieces during work, said measuring means having a branch conduit connected to said main conduit, the control conduit being connected with the branch conduit delivering the measuring pressure for operating dependently upon the measuring pressure the amplifier and the utilization means to control a stage of the operational cycle of the machine.

8. The combination defined in claim 7, wherein the utilization means includes switches for an associated machine tool circuit.

9. Fluid amplifier as claimed in claim 1, wherein an outwardly opening pipe is branched from the main conduit, provided with a calibrated nozzle at its free end and a throttle intermediate its free end and the main conduit, the control conduit being derived from a section of the said branch pipe intermediate the throttle and calibrated nozzle, the nozzle being adapted to cooperate with a surface turned towards the nozzle in order to determine distance thereof.

10. The combination defined in claim 1, including a variable throttle valve and an intercepting valve in said control conduit, a capacitive tank for the control fluid being located intermediate the throttle valve and intercepting valve.

11. The combination as defined in claim 1, including a blind conduit derived from the control conduit to provide an oscillator.

12. The combination as defined in claim 11, wherein the said blind conduit has at least one turn at its section intermediate the blind end and connection to the control conduit.

13. A fluid amplifier providing a sensitive switching function, comprising: a supply conduit, a first outlet conduit, a second outlet conduit, said conduits being positioned so that in the absence of other influences supply fluid flow in said supply conduit will exit through said first conduit thereby giving the amplifier a monostable characteristic, utilization means communicating with said second conduit and responsive to fluid pressure therein, a control conduit for supplying fluid to switch the supply fluid from said first outlet to said second outlet, means providing sensitive switching from said first conduit to said second conduit including means for feeding back substantially all of the fluid in said first outlet toward a region of interaction between the control fluid and the supply fluid, and means for directing the feedback fluid to oppose the influence of said control fluid on the supply fluid whereby when the control fluid overcomes the influences of the monostable characteristic of the amplifier, supply fluid will be rapidly switched to said second outlet at a predetermined pressure of control fluid.

14. A fluid amplifier as defined in claim 13, including means for varying the feedback fluid to vary the control fluid pressure at which the main supply will switch to the second outlet.

References Cited UNITED STATES PATENTS 3,425,430 2/1969 Horton 137-81.5 3,001,539 9/1961 Hurvitz 137-815 3,131,601 5/1964 Curran 137-815 3,158,166 11/1964 Warren 137-815 3,217,727 11/1965 Spyropoulos 137-815 3,241,668 3/1966 Schonfeld et al 137-815 3,241,669 3/1966 Schonfeld et al. 137-815 3,244,370 4/1966 Colston 137-815 M. CARY NELSON, Primary Examiner W. R. CLINE, Assistant Examiner 

